Stainless steels microstructure

Figure 1.10 Photo and details of a stainless steel microstructure cube generated bySLM method. Clearly, the single welding beads that have been generated layer by layer to form the walls are shown.

Duplex stainless steels contain both ferrite and austenite in approximately equal amounts Alloy 2205 is an example. Figure 21.9 illustrates the microstructure of a duplex stainless steel microstructure in plate material. Typically, the duplex stainless steels contain 17 wt% or more chromium and <7% nickel. The more corrosion-resistant types contain at least 2% molybdenum. They are much stronger than the austenitic stainless steels, permitting a thinner section thickness. Thus, while they may cost more per pound, they may cost less per piece. 

Hor] Horovitz, M.B., Neto, F.B., Garbogini, A., Tschiptschin, A.P., Nitrogen Bearing Martensitic Stainless Steels - Microstructure and Properties , ISIJ Int., 36(7), 840-845 (1996) (Experimental, Meehan. Prop., Morphology, 14)... 

To overcome these medium- to long term substrate degradation issues, the surface of the structured material has to be properly prepared and protected during the phase of assembly and catalyst coating. This feature is so important that, as mentioned before, almost no relevant and detailed long-term studies have been reported yet on the corrosion effects on stainless-steel microstructured platelets. 

Figure 4J Experimental temperature profile measured for the steam reforming of methane in a stainless-steel microstructured reactor at 800°C...

De Las Heras E, Egidi DA, Corengia R Gonzalez-Santamaria D, Garcfa-Luis A, Brizuela M., Lopez GA, Flores Martinez M. (2008) Duplex surface treatment of an AISI 316L stainless steel Microstructure and tribological behaviour. Surf Coat Technol 202 2945-2954. 

Microstructural examinations revealed that the cracks originated on the external surface (Fig. 9.15). The cracks were highly branched and transgranular. The branched, transgranular character of these cracks is typical of stress-corrosion cracking of austenitic stainless steels. The thick-walled fracture faces are also typical of cracking by this mode. 

Microstructural examinations disclosed highly branched, predominantly transgranular cracks originating on the internal surface. Cracks of this form are typical of SCC in austenitic stainless steels. 

Dents in tubing can induce erosion failures, especially in soft metals such as copper and brass. Welding and improper heat treatment of stainless steel can lead to localized corrosion or cracking through a change in the microstructure, such as sensitization. Another form of defect is the inadvertent substitution of an improper material. 

Most defects can be detected using one or more appropriate nondestructive testing techniques. However, in the absence of routine nondestructive testing inspections, identification of defects in installed equipment is generally limited to those that can be observed visually. Defects such as high residual stresses, microstructural defects such as sensitized welds in stainless steel, and laminations will normally remain undetected. Defects that can be detected visually have the following features ... 

Galvanic corrosion may occur at stainless steel welds if sensitization has taken place or if welding has produced unfavorable dissimilar phases (see Chap. 15, Weld Defects, particularly Case History 15.1). These forms of microstructural galvanic corrosion do not involve the joining of two different metals in the usual sense. 

Streicher, M. A., Effect of Heat Treatment, Composition and Microstructure on Corrosion of 18Cr-8Ni-Ti Stainless Steel in Acids , Corrosion, 20, 57t (1964)... 

Similarly it seems that retained austenite may be beneficial in certain circumstances , probably because the austenite acts as a barrier to the diffusion of hydrogen, although in high concentrations (such as those obtained in duplex stainless steels) the austenite can also act as a crack stopper (i.e. a ductile region in the microstructure which blunts and stops the brittle crack). 

A magnetic form of stainless steel that contains an aFe microstructure. 

Fabrication was done by photolithography and deep reactive ion etching (DRIB). The catalyst was inserted by sputtering. Such a prepared microstructure was sealed with a Pyrex cover. The bonded micro device was placed on a heating block containing four cartridge heaters. Five thermocouples monitored temperature on the back side. A stainless-steel clamp compressed the device with graphite sheets. 

A caterpillar steel mini mixer can be connected to conventional tubing, either stainless steel or polymeric, to prolong the residence time. The caterpillar mixer as all types of split-recombine mixers, profits from high volume flows (e.g. 100 1 h and more at moderate pressure drops) at favorable pressure drop (not exceeding 5 bar) as its internal microstructures can be held large [25-28]. 

A wide range of stainless steels is available, with compositions tailored to give the properties required for specific applications. They can be divided into three broad classes according to their microstructure ... 

T. Ohmura, K.Tsuzaki, K. Sawada, and K. Kimura, Inhomogeneous Nanomech-anical Properties in the Multi-phase Microstructure of Long-term Aged Type 316 Stainless Steel, Jour. Mater. Res., 21,1229 (2006). 

Tritium and its decay product, helium, change the structural properties of stainless steels and make them more susceptible to cracking. Tritium embrittlement is an enhanced form of hydrogen embrittlement because of the presence of He from tritium decay which nucleates as nanometer-sized bubbles on dislocations, grain boundaries, and other microstructural defects. Steels with decay helium bubble microstructures are hardened and less able to deform plastically and become more susceptible to embrittlement by hydrogen and its isotopes (1-7). 

Figure 5. Typical Microstructures of Forged Type 21-6-9 Stainless Steel (Oxalic Acid Etch, 90 s) (a) Conventionally Forged and, (b) High-Energy-Rate Forged.

M. H. Tosten and M. J. Morgan, Microstructural Study of Fusion Welds in 304L and 21Cr-6Ni-9Mn Stainless Steels (U) , WSRC-TR-2004-00456, March, 2005... 

M. J. Morgan and M. H. Tosten, "Microstructure and Yield Strength Effects on Hydrogen and Tritium Induced Cracking in HERF Stainless Steel", Hydrogen Effects on Material Behavior, ed. N. R. Moody and A. W. Thompson, (Warrendale, PA TMS, 1990), 447-457. 

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